A) 5V needs more than one cell in schematic, not sure why it would be in parallel with a voltage source of same polarity, unless I'm missing something.
B) The two current sources short each other out
C) DC will only provide a pulse to the load through the transformer at power on, then nothing.

If the voltage across the two batteries is exactly equal then no problem exists with no load on the output.
If the batteries have slightly different voltages then current will flow between them until the voltage on both becomes equal.
If you connect a load and the batteries have different internal resistance, Ah rating and temperature coefficient then the one will discharge faster and current will circulate between the batteries.

For circuit (b):

If the current sources have exactly equal output current then the output voltage will be zero otherwise the output voltage will be infinite.

For circuit (c):

A DC voltage does not create a time varying flux and thus the transformer won't produce a voltage on its secondary. Also, a large current will flow through the primary, depending on its dc resistance, and blow the transformer or the DC source.